/// <summary>
/// Gets the corresponding CRC table for the given polynomial.
/// </summary>
/// <param name="polynomial">The polynomial to get a CRC table for.</param>
/// <param name="cacheCrcTable">Whether or not to cache the generated CRC table in <see cref="CrcTables"/>.
/// If this CRC is used as the starting point for others, the CRC table will be carried over from it.
/// The cache is only used if this constructor is called again with the same polynomial.</param>
/// <returns></returns>
private static CrcTable GetCrcTable(uint polynomial, bool cacheCrcTable)
{
if (!CrcTables.TryGetValue(polynomial, out var crcTable))
{
crcTable = new CrcTable(polynomial);
if (cacheCrcTable)
{
CrcTables[polynomial] = crcTable;
}
}
return(crcTable);
}
/// <summary>
/// Updates a CRC value directly.
/// </summary>
/// <param name="crc">The CRC to update.</param>
/// <param name="b">The byte to update the CRC with.</param>
/// <param name="crcTable">The CRC table to use when updating the CRC.</param>
/// <returns></returns>
private static uint UpdateCrc(uint crc, byte b, CrcTable crcTable)
{
return(crc = (crc >> 8) ^ crcTable[(crc ^ b) & 0xFF]);
}
/// <summary>
/// Instantiates a new <see cref="Crc32"/>.
/// </summary>
/// <param name="crc">The value of the CRC.</param>
/// <param name="correspondingCrcTable">The CRC table that will be used, based on its polynomial.</param>
/// <param name="finalXor">The final XOR value to apply to the CRC before returned.</param>
private Crc32(uint crc, CrcTable correspondingCrcTable, uint finalXor)
{
Crc = crc;
CorrespondingCrcTable = correspondingCrcTable;
FinalXor = finalXor;
}
